It is difficult for a conventional speaker system using a small cabinet to reproduce low frequency sound because of an influence of acoustic stiffness caused by a space in the cabinet. The limit of low frequency sound reproduction depends on a magnitude of acoustic stiffness, that is, a volume of the cabinet. As means for solving the problem associated with the limit of reproduction, suggested is a speaker device in which a gas adsorber for physically adsorbing gas is provided in the cabinet (for example, refer to Patent Document 1).
FIG. 15 is a partial cross-sectional view illustrating a main portion of a conventional speaker system 9. In FIG. 15, the speaker system 9 includes a cabinet 90, a speaker unit 91, a gas adsorber 92, and bags 93. The cabinet 90 includes a plane-plate shaped front wall 901 and curved side walls 902. The speaker unit 91 is an electrodynamic speaker. Driving force generation means of the speaker unit 91 includes a magnetic circuit and a voice coil. The speaker unit 91 is mounted on the front wall 901. The gas adsorber 92 is simply an activated carbon 921 including a plurality of grains as shown in FIG. 16. FIG. 16 is a diagram illustrating a structure of the conventional gas adsorber 92. The grains of the activated carbon 921 each includes multiple pores, and gas (molecule of gas) is physically adsorbed into the pores. The gas adsorber 92 is enclosed in the bags 93 having a tube shape determined by molding. The bags 93 are positioned in the cabinet 90 in curved portions of the side walls 902.
An operation performed by the speaker system 9 having a configuration as described above will be described. When a music signal is applied to the speaker unit 91, a driving force is generated in the voice coil, and the generated driving force causes a diaphragm to vibrate. Thus, sound is emitted from the front surface and the back surface of the speaker unit 91. The sound emitted from the back surface of the speaker unit 91 changes gas pressure in the cabinet 90. However, the cabinet 90 includes the gas adsorber 92 therein. Therefore, when the gas pressure changes in the cabinet 90, gas is physically adsorbed in the gas adsorber 92 so as to suppress the change in gas pressure. Therefore, the cabinet 90 operates as a cabinet equivalent to a cabinet having a great volume. As described above, in the conventional speaker system 9, the physical adsorption of gas into the gas adsorber 92 is equivalent to an increase of the volume of the cabinet 90. As a result, low frequency sound reproduced by a speaker unit mounted in a large cabinet can be obtained in a small cabinet. Hereinafter, an effect obtained by the equivalent increase in volume of a cabinet is referred to as a volume increase effect.    Patent Document 1: Japanese Translation of PCT international application No. 2004-537938